1. Field of the Invention
The present invention relates to an image sensor in which focus detecting pixels are arranged on an imaging plane for performing focus detection by a phase difference method.
2. Description of the Related Art
There has been conventionally known an image sensor in which a focus detecting pixel is arranged at apart of the image sensor for performing focus detection by a phase difference method. For example, Japanese Patent Laid-Open No. 2013-257494 (hereafter referred to as “PTL 1”) discloses an image sensor in which a right opening pixel (called R-pixel in abbreviation) to cause a subject light flux from the right side to enter the pixel and a left opening pixel (called L-pixel in abbreviation) to cause a subject light flux from the left side to enter the pixel are arranged in the horizontal direction as focus detecting pixels.
Since the R-pixel and the L-pixel are arranged only in the horizontal direction in PTL 1, when a subject having a contrast change only in the horizontal direction is inclined in an angle not smaller than 45 degrees from the horizontal direction, for example, it is not possible to perform photometry for the subject to detect the contrast change. Accordingly, a top opening pixel (called T-pixel in abbreviation) to cause a subject light flux from the upper side to enter the pixel and a bottom opening pixel (called B-pixel in abbreviation) to cause a subject light flux from the lower side to enter the pixel are arranged in the vertical direction, and thereby it could become possible to perform photometry also for the subject inclined in an angle not smaller than 45 degrees.
When the T-pixels and the B-pixels are arranged at G-pixel (pixel where a green color filter is arranged) positions in the same level density as the R-pixels or the L-pixels, however, it is difficult to secure a sufficient image quality in moving image photographing in which mixing readout is performed. That is, the focus detecting pixel has a pixel value different from a normal imaging pixel for a uniform light flux on the imaging plane because a light blocking part exists for forming an opening. Therefore, in the mixing readout, when the pixel value of the imaging pixel and the pixel value of the focus detecting pixel are mixed, it is necessary to perform correction or the like, and it is difficult to secure a sufficient image quality even when the correction is performed.